One of the world’s most productive Earth-observing satellite appears to have finally reached the end of its mission.

While Envisat remains in a stable orbit around Earth, it suddenly stopped transmitting images on April 8, 2012.

Engineers at the European Space Agency, which operates the satellite, have continued to monitor other aspects of Envisat in an attempt to pin down the cause of the blackout.

But Mission Manager Henri Laur says he is pessimistic about prospects of receiving any more data.

The image to the right of the Iberian Peninsula, taken at 2:05 p.m. Central European Time on April 8, was the last of its kind received by ground stations. A final radar image was received four minutes later.

Envisat was designed to operate for only five years but had remained reliable for twice that period before suddenly going dark.

During that time, its 10 instruments provided scientists with critical data on such environmental features as air quality, sea level rise, oil spills, Arctic sea ice coverage as well as climate change.

It was scheduled to be replaced over the next few years by a constellation of five new satellites in a program called GMES (Global Monitoring for Environment and Security) Sentinel. But the first one is not expected to be ready for launch until late next year.

So until that time, a Canadian satellite will provide less detailed radar images to replace those from Envisat. NASA’s Terra, Aqua and various other earth-observing satellites will also ensure that critical elements of Earth's environment will continue to be monitored.